Cultivation of micro-organisms on a feedstock consisting at least in part of straight chain hydrocarbons

ABSTRACT

The present invention is directed to an improved hydrocarbon fermentation process which comprises cultivating a straight chain paraffinic hydrocarbon consuming micro-organism in the presence of a feedstock consisting at least in part of a straight chain hydrocarbon, recovering a fraction comprising the micro-organism and at least some aqueous medium and residual hydrocarbon, adding a surface active agent and subjecting the resulting mixture to phase separation to recover (a) a treated fraction comprising the micro-organism together with an aqueous phase and some residual hydrocarbon fraction and (b) a hydrocarbon fraction and subjecting the treated fraction to solvent extraction to remove lipids and associated hydrocarbons from said microorganism.

United States Patent [191 Champagnat et al.

[111 3,847,739 1 Nov. 12, 1974 CULTIVATION OF MICRO-ORGANISMS ON AFEEDSTOCK CONSISTING AT LEAST IN PART OF STRAIGHT CHAIN HYDROCARBONS v[75] Inventors: Alfred Champagnat, Courbevoise;'

Bernard Maurice Laine, Lavern, both of France [73] Assignee: The BritishPetroleum Company Limited, London, England [22] Filed: May 21, I973 [21]Appl. No.: 362,063 i Related U. S. Application Data [63] Continuation ofSer. No. 69,474, Sept. 3, I970, abandoned, which is a continuation ofSer. No.

845,662, July l0, i969. abandoned, which is a continuation of Ser. No.546,607, May 2, 1966,

abandoned. v

5 2 U.S..Cl. 195/28 195/82 [51] Int. Cl Cl2b 1/00 [58] Field of Search195/28 R, 3

[56] References Cited UNITED STATES PATENTS 3,186,962 6/1965 Champagnatet al 195/82 OTHER PUBLICATIONS Raymond R. L., Microbial Oxidation ofn-Paraffine Hydrocarbons, Developments In Industrial Microbiology, Vol.2, pp. 23-32.

Primary Eraminer-Lionel M. Shapiro Assistant ExaminerR. B. PenlandAttorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine [57] ABSTRACTThe present invention is directed to an improved hydrocarbonfermentation process which comprises cultivating a straight chainparaffinic hydrocarbon con- 19 Claims, No Drawings This is acontinuation of applicationSer. No. 69,474

filed Sept. 3, 1970, abandoned; which isacontinuation The cultivation ofyeasts on hydrocarbons, andfin' particular on petroleum hydrocarbons, asthe carbonaceous substratum, generally gives yeasts-which after washingand drying-possess a peculiar-taste which is sharp and rancid andwhich-may interfere with their use in foods for human consumption. Thetraditional yeasts, cultivated on molasses, residuary liquors orbisulphite liquors, alsohave apeculiar taste, different from that ofyeasts cultivated on hydrocarbons, and certain processes have beenproposed for attenuating this taste notabl-yto attenuate theirbi'tterness, bu-t none of these has succeeded completely.

It has now been found thatyeasts cultivated with hydrocarbons as thesole source of carbon have a distinctly higher lipid contentthanyeastscultivated .on the traditional substrata: molasses, residuary liquors,bisulphite liquors. Lipids consist-essentially of fatty acids, esters(with greater or lesser degrees of oxidation) including fats andsterols. It has now beenfound that extraction-of theselipids, wholly orin part, leads to a sub.-

stantial reduction in this characteristic taste of yeasts cultivated onhydrocarbons, or totheelimination ofthis taste.

It is an object of this invention to provide animproved process for theproductionof micro-organisms. [t is a further object to provide aprocessfor the production of a yeast. It is a further object to provide aprocess for theremoval of straight chainhydrocarbons, wholly or in part,from .mixtures of said hydrocarbons .with other hydrocarbons. Otherobjects will appear hereinafter.

According to one aspect of this invention there is provided a processwhich comprises cultivating a micro-organism capable of growing on afeedstock consisting wholly orin part of straight'chain hydrocarbonswith formation of lipids, said micrmorganism beingqcultivated in the.presence of said feedstock, separating from the product a fractioncomprising the micro-v organism and extractingsaidfraction by means of-asolvent to removelipids in thexextractphase.

Suitably, in accordance with the invention, straight chain hydrocarbonsare removed from a petroleum fraction with production of amicro-organism, wherein the feedstock employedfor the growth of themicroorganism is a petroleum fraction consisting inipartof straightchain hydrocarbonswherein there is recovered from the product of thegrowth ofthe micro-organism I, a petroleum fraction having a. reducedproportioniof straight chain hydrocarbons or which is free of saidstraight chain hydrocarbons. The process of the invention isparticularly suitable for the removal, wholly or in part, of waxes froma wax-containing petroleum gas oil, wherein the feedstockisjawax-containingpetroleum gas oil and wherein thereisrecovered, from theproductof the: growth of the micro-organism,'a-gas oil of reducedcontentof wax.

Solvents which maybe employed in the solvent extraction stagein-accordance with theinvention include ethyl alcohol, iso-propanol,light hydrocarbons,including benzene andlightplatformatefractions, ethylether, acetone, chlorinatedsolvents and-liquefied petroleum gases suchas butane and propane.

Within the term micro-organism" used herein we include mixtures ofmicro-organisms.

Micro-organisms which are-cultivated; as ,herein described may beyeasts,-moulds orbacteria capable of growing on-astraight-chain@hydrocarbon.

Preferably :when-a-yeast: is employed this is of the family,Cryptococcaceae and particularly of the subfamilyCryptococcoideae;however, if desired there may be-used; foryexample, ascosporogeneousyeasts of the .-su-b-famil y Saccharom-ycoideae. Preferred genera of"the Cryptococcoideae familyare Torulopsis (also known as Torula) ,:;Candi.d.a.and'Mycoderma. Preferred strainsof ,yeastare asfollows. Inparticular it is preferred toluse IhC SpCGll' lCQSIOCk of indicatedreference number; these referencev numbers refer-to CBS stock heldby theCentfiaalBure-au vor ,Schimmelculture, Baarn, Hollandandto lNR-Astockheldby thelnstitut Nationalv de la Recherche Agronomique, Paris, France.

cancoillule Of the above Candida lipolytica is particularly preferred.

If desired, the micro-organism .may be a mould. A suitable strain isPenicillium expansum.

lf desired, the micro-organismimay be a bacterium.

uitably the acteria. are of :one of the orders:Paeudomonales,Eubacterialesand-Actinomycetales.

Rreferably the. bacteria which are employed are of the,familyBacillaeeae and Pseudomonadaceae. ,Rreferred species are-Bacillusme gaterium, Bacillus subtllis and ,Pseudomonas 'aeruginosa. Otherstrains which may be,emloy e d.include:

Bacillus amylobacler Pseudanzonas' narriegens Arrhrebacrer sp.Micrococcus sp. Coryaebacterium mic/rigauemre Pseudomonas syringaeXamlwmrmas beguniae Flavobacteriumdevoranx Avewbacler .\'[J.Aclononrw'cr sp. Agruhacl 'rium .i'p. Aplanobai'lcr .rp.

For the growth of the micro-organism it will be necessary to provide, inaddition to the feedstock, an aqueous nutrient medium and a supply ofoxygen, preferably in the form of air.

A suitable nutrient medium for yeasts (and moulds) 5 has thecomposition:

Diammonium phosphate 2 grams Potassium chloride l.l5 grams Magnesiumsulphate, 7H O 0.65 grams 10 Zinc sulphate 0.17 grams Manganesesulphate, IH O 0.045 grams Ferrous sulphate, 7H O 0.068 grams Tap water200 grams Yeast extract 0.025 grams Distilled water (to make up to l000mls.)

A typical nutrient medium for the growth of Necardia, a genus in theActin omycetales order, has the following composition:

Ammonium sulphate 1 gram Magnesium sulphate 0.20 grams Ferrous sulphate,7H O 0.005 grams Manganese sulphate, lH O 0.002 grams Monopotassiumphosphate 2 grams Disodium phosphate 3 grams Calcium chloride 0.1 gramsSodium carbonate 0.1 grams Yeast Extract 0 008 grams Distilled water (tomake up to 1000 mls.)

For other bacteria a suitable nutrient medium has the composition:

Monopotassium phosphate 7 grams Magnesium sulphate, 7H O 0.2 gramsSodium chloride 0.1 grams Ammonium chloride 2.5 grams Tap water (traceelements) 100 mls Yeast extract 0.025 grams Made up to I000 mls, withdistilled water Another suitable nutrient medium for the growth ofbacteria has the composition:

NH Cl 0 5 grams NaCl 4 grams MgSO, 0.5 grams Na HPO, 0 5 grams KH PO 0 5grams Water to make up to: I000 mls Micro-organisms, and in particularyeasts, when first cultivated with the use of hydrocarbon fractions asfeedstock sometimes grow with difficulty and it is sometimes necessaryto use an inoculum of a microorganism which has previously been adaptedfor growth on the hydrocarbon fraction which it is intended to use.Furthermore the micro-organism although cultivated in the presence of anaqueous mineral medium containing the appropriate nutrient elements maygrow with difficulty, because the hydrocarbon fraction does not containthe growth factors which exist in carbohydrate feedstocks, unless thesegrowth factors are added.

In batch operation, the micro-organism will usually grow initially at alow rate of increase in cellular density. (This period of growth isreferred to as the lag phase). Subsequently the rate of growth willincrease to a higher rate of growth; the period at the higher rate ofgrowth is referred to as the exponential phase and subsequently againthe cellular density will become constant (the stationary.phase).

A supply of the micro-organism for starting the next batch willpreferably be removed before the termination of the exponential phase.

The growth operation will usually be discontinued before the stationaryphase.

At this stage, the micro-organism will usually be separated from thebulk of the aqueous nutrient medium and from the bulk of the unusedfeedstock fraction.

The growth of the micro-organism used is favoured by the addition to theculture medium of a very small proportion of extract of yeast (anindustrial product rich in vitamins of group B obtained by thehydrolysis of a yeast) or more-generally of vitamins of group B and/orbiotin. This quantity is preferably of the order of 25 parts per millionwith reference to the aqueous fermentation medium. It can be higher orlower according to the conditions chosen for the growth.

The growth of the micro-organism takes place at the expense of thefeedstock fraction with the intermediate production of bodies having anacid function, principally fatty acids, in such manner that the pH ofthe aqueous mineral medium progressively diminishes. If one does notcorrect it the growth is fairly rapidly arrested and the concentrationof the micro-organism in the medium, or cellular density, no longerincreases so that there is reached a so-called stationary phase.

Preferably therefore the aqueous nutrient medium is maintained at adesired pH by the step-wise or continuous addition of an aqueous mediumof high pH value. Usually, when using moulds or yeasts and in particularwhen using Candida lipolytica, the pH of the nutrient medium will bemaintained in the range 3-6 and preferably in the range 4-5. (Bacteriarequire a higher pH usually 6.5-8). Suitable alkaline materials foraddition to the growth mixture include sodium hydroxide, potassiumhydroxide, disodium hydrogen phosphate and ammonia, either free or inaqueous solution.

The optimum temperature of the growth mixture will vary according to thetype of micro-organism employed and will usually lie in the range 2535C. When using Candida lipolytica the preferred temperature range is 2832C.

The take-up of oxygen is essential for the growth of the micro-organism.The oxygen will usually be provided as air. In order to maintain a rapidrate of growth the air, used to provide oxygen, should be present in theform of fine bubbles under the action of stirring. The air may beintroduced through a sintered surface.

' However there may be used the system of intimate aeration known asvortex aeration.

It has been found that by the use of yeast of the strain Candidalipolytica in a process according to the invention in which aeration iseffected by vortex aeration, a high growth rate is achieved whereby thegeneration time lies in the range 2-5 hours and the cell concentrationis increased by a factor of up to 12 in 2 days.

The micro-organism is preferably separated from the bulk of the liquidphase when possible by centrifuging and may be recovered as a cream orpaste. However, in some cases separation will be accomplished byfiltration or to some extent by decantation.

This cream or paste which contains aqueous material may be treated bycontinuous solvent extraction or by successive washings with solventfollowed by phase separation. Suitably the extraction is carried out ina stationary vessel equipped with paddle stirrer s, preferably rotatingat less than revs per minute or in'a vessel which rotates on ahorizontal axis. When operating a continuous solvent extraction, theextract is withdrawn continuously and distilled, continuously orbatchwise, at atmospheric or reduced pressure, and solvent continuouslyfed back to the extractor. Under these conditions the yeast may beintroduced and withdrawn continuously or batchwise.

Preferably the solvent extraction. is effected while feeding solvent tothe extractor at a periodically varying rate to create pulsations inthe. flow of said liquid stream.

The pulses of the liquid passing throughthe solid: material bring aboutoscillations and. limited displacements of each. grain of solid materialin relation to its neighbours, and this is equivalent to a mechanicalagitation of the whole. For this'reason the whole of the products to beextracted is much. more rapid and complete.

Suitably there is arranged in. the feed of the liquid stream a devicewhich imparts to it pulses whose amplitude and frequency are regulatedexperimentally at the most favourable value for each particular case.These pulses are produced by any suitable processes already known, andpreferably an alternating pump is used whose valves have been removed.

Preferably the number of pulses lies between 1 and 60 per minute. Theoperation of the process under the action of pulses is further describedin British Patent Application 2234/63..-

Suitable solvents for use in the process have been describedhereinbefore. If desired a first extraction stage can be operated usinga polar solvent, for example an alcoholic solvent, for example ethanolor isopropanol and then the partially purified micro-organism can befurther treated in a second. extraction stage using a hydrocarbon.solvent, for example normal hexane or a light platformate fraction orbenzene.

Preferably in the second stage there is used as solvent a mixture of ahydrocarbon in major amount with a polar solvent in minor amount.Preferably there is used the azeotropic mixture of hexane withisopropanol or ethanol. If desired both extraction stages can beoperated in' continuous manner.

When using a solvent consisting of a mixture of a hydrocarbon and apolar solvent, it is believed that the function or onefunction of thepolar solvent is to weaken the bonding of the material to be extracted(even the bonding of hydrocarbons which are not themselves soluble inthe polar solvent).

By the use of any alcohol in the first stage of a two stage extractionas hereinbefore described, the water content of the micro-organism creamor paste is considerably reduced. As a result the micro-organismcontaining material which is fed to the'second stage has a sufficientlylow content of water to ensure that the nonaqueous contaminants whichare still present are miscible with the solvent used in the secondextraction stage. Each extraction stage may consist of either one ormore sub-stages consisting of washing with the solvent used in the stagefollowed by separation.

If a single washing is employed in the first stage the amount of ethanolor isopropanolwhich is used should be 1.5 3 times the volume of waterwhich is present in the cream or. paste of the micro-organism. Howeverif desired two washings with ethanol or isopropanol may be employedusing in the first washing a volume of solvent equal to the volume ofwater in the. cream or paste and in the second washing a smaller amountof ethanol or isopropanol for example, one half of the amount used inthe first washing.

Between washings of each stage or sub-stage the cream or paste isallowed to drain, for example by filtering and part of the residualsolvent is then preferably removed, by vacuum filtration.

In the second stage the amount of solvent used in the (or each) washingwill usually be 2-20 times the volume of the resulting drymicro-organism;

Preferably the final stage employed for the removal of solvent isevaporation, suitably under reduced pressure and suitably in a stream ofinert gas, for example, nitrogen or super-heated steam.

By the use in the second extraction stage of a solvent whichis a mixtureof a hydrocarbon and a polar solvent the composition of the second stagesolvent, which will in any case acquire polar solventfrom the firststage extraction, can be-stabilised. Build up of polar solvent can beavoided. in the course of a distillation stage, in which the secondstage solvent is recovered by the removal of separate streams consistingof (a) polar solvent for recycle to the first extraction stage and (b) amixture of a hydrocarbon and polar solvent for recycle to the secondstage. Suitably in a distillation stage the extract obtained bythesecond extraction stage is distilled to recover (a) overhead amixture of a hydrocarbon, polar solvent and water for recycle to thesecond extraction stage and (b) a bottoms fraction containing polarsolvent, water and the extracted materials; this fraction is preferablyblendedwiththe extract obtained in the first extraction stage beforethis is fed to distillation whereby all contaminants recovered bysolvent extraction are removed as a bottoms fraction in thisdistillation stage. Suitably ,the polar solvent is ethanol orisopropanol. Suitably the second stage solvent is an azeotropic mixture.

In accordance with preferred procedure the microorganism containingfraction is treated in a first stage consisting of one or moresub-stages, in each sub-stage the fraction being washed with a polarsolvent and the extract separated, one or more extract fractions beingblended with a second stage recycle fraction and the blend distilled torecover first stage solvent which is recycled and a residue fraction,the raffinate product of the first stage being passed to. a second stagetreatment, consisting of one or more substages, in each sub-stage thefraction being washed with a mixture of a hydrocarbon solvent and apolar solvent and the extract separated, one or more second stagefractions being distilled with recovery of a. a first stage solventwhich is recycled to the first stage,

b. a fraction containing hydrocarbon solvent and polar solvent which isrecycled to the second solvent extraction stage and c. a bottomsfraction containing extracted materials which constitutes the saidsecond stage recycle fraction.

Optimum contact time will usually vary inversely with thetemperature ofextraction. It will usually be undesirable to use a temperature above Csince higher temperatures will lead to some degradation of the product.

If the cream or paste of micro-organism is subjected to partial dryingbefore solvent extraction it will then usually be possible to operatethe first extraction stage with only a single washing with an alcoholicsolvent and with the use of a smaller amount of solvent than would berequired if no drying had taken place. If the extent of drying isconsiderable a first extraction stage using a polar solvent, for examplean alcoholic solvent, is not necessary; in this case the single stageextraction process can be operated by the use of a solvent which isentirely hydrocarbon or which is a mixture of a hydrocarbon and polarsolvent, for example an alcohol ketone or chlorinated hydrocarbon.

In general it is desirable to avoid drying under drastic conditionssince this will lead to partial decomposition of the micro-organism, forexample by destruction of vitamins and oxidation of unsaturatedcompounds; furthermore the products of decomposition will be soluble inthe solvent used in extractive distillation thus being lost from theproduct or requiring further stages for their recovery.

A yeast which has been freed from the whole or part of its lipids andthe contaminating hydrocarbons by one of the methods describedhereinbefore and whose taste has been improved is a new industrialproduct of value for human nutrition.

The lipid extract which has been recovered by the evaporation of thesolvent is also a new industrial product which can be used either assuch or as a raw material for the separation of its sterols, fatty acids(either before saponification or after) or of its other constituents.

The invention is illustrated but not limited by the following Examples1-6. Experiments 1 and 2 which do not constitute operation according tothe invention are provided for purposes of comparison.

EXAMPLE 1 litres of the following aqueous mineral medium was introducedinto a litre stirred fermenter; parts are by weight:

Sodium phosphate, tribasic 3.4 Potassium chloride 0.6 Magnesium sulphate0.3

Ammonium sulphate 2. Made up to 1000 parts with soft water containingtrace elements.

A suitable alternative medium has the composition:

Diammonium phosphate 2 Potassium chloride l.l5 Magnesium sulphate, 7H O0.65 Zinc sulphate 0.17 Manganese sulphate, 1 H O 0.045 Ferroussulphate, 7 H O 0.068 Tap water 200 Yeast extract 0.025

Distilled water (to make up to I000 parts).

To the fermenter was added a few parts per million of yeast extract andthen 50 grams of Candida lipolytica in the form of an aqueous creamcontaining percent by wt. of dry material and then 150 grams of a heavygas oil of petroleum origin containing 20 percent by wt. of normalparaffms.

When the culture reached the desired concentration of yeast cells forcontinuous operation, the continuous feed, to the fermenter, of aqueousmineral medium and petroleum oil was started up. The temperature wasmaintained at 30 C and the pH of the medium was maintained regulated atpH 4 by the addition of aqueous ammonia.

This emulsion was fed to a centrifugal separator from which wererecovered three phases, being, in increasing order of density; (a) anoil phase containing the yeast cells, (b) an aqueous mineral mediumphase (which may contain traces of oil and yeast) and (c) a yeast creamcontaining approximately 1 part of yeast, 4 parts of aqueous medium anda certain quantity of oil adhering to the yeast cells.

The yeast cream together with an aqueous solution of a surface activeagent, for example a non-ionic detergent having, in the molecule, acondensed ethylene oxide chain, was fed continuously to a mixer and themixture so obtained was centrifuged to obtain three fractions: inincreasing order of density: (a) an oil phase, (b) an aqueous phasecontaining the surfactant product which was recycled to the mixer and(c) a second yeast cream containing 1 part by wt. of yeast (which wasstill slightly contaminated by the oil) with 4 parts by wt. of aqueousliquid containing the surfactant.

This second yeast cream was passed with water to a mixer and the mixtureso obtained was centrifuged to obtain: (a) an oil phase, (b) an aqueousphase and (c) a thick yeast cream containing 20 percent by wt. of yeast(estimated as dry yeast) and percent by wt. of water and which containedonly a very small quantity of oil.

This thick yeast cream contained 44 percent by wt. of proteins and 18.5percent by wt. of lipids. lt possessed a sharp and rancid taste. Thelipids with residual oil were extracted from the yeast by solventextraction using a mixture of 80 percent of hexane and 20 percent ofethyl alcohol.

After evaporating the solvent, a yeast containing 52 percent of proteinsand 3 percent of lipids was obtained.

(From gms. of yeast there was obtained by solvent extraction 16 gms. ofextract consisting principally of oxidised and unoxidised fatty acids,esters and sterols.)

The yeast which had thus been freed from the major part of its lipidspossessed a neutral taste.

EXAMPLE 2 Solvent was drawn off, finally under vacuum. There was thusobtained a mixture of 2 parts of yeast and 2 parts of solvent whichconsisted of /a water and of ethanol, together with some remainingcontaminants.

This mixture was treated with 10 parts by weight of a solvent mixtureconsisting of:

Normal Hcxane Ethanol 80% by Wt. 207: by wt.

The mixture was maintained at 60 C for 15 minutes and solvent drawn off,finally under vacuum. The wash- Table Yeast cream Yeast productNitrogen, by wt. of 7% 7.8% dry yeast Total wt. of Lipids 0.5% based onwt. of dry yeast EXAMPLE 3 The yeast cream described in Example 2 wascontinuously extracted in a'drum havingits axis vertical and having apaddle stirrer which rotated at 10 revs/minute.

In separate runs the solvent'was respectively ethanol; ethanol followedby normal hexane; and isopropanol.

The extractwas continuously distilled forthe recovery of lipids andhydrocarbons andthe solvent recycled to the extractor. V

Conditions and results obtained were as shown in the dium containing 0.5grams/litre of a non'ionic surface active agent consisting'ofthecondensation productof 1 mole of lauric alcohol with'8.75 mole ofethyleneoxide. The mixture isfed to aSharples Super centrifuge (oftubular type).

The micro-organism containing fraction obtained from the centrifuge isafterwards washed withtap-water only. The cream containing 1 part byweight'of yeast (estimated as dry yeast after dryingat 120 C) and 3.5parts by weight of water is charged to a solvent extrac tor drum with 8parts by :weight of isopropanol. The mixture is maintainedat 60 C forminutes while rotating the drum.

Solvent is drawn off finallyunder vacuum. There is thus obtained amixture of 1 part of dry matter and 1 part of solvent which consists of/a of water and /3 of isopropanol together with some remainingcontaminants.

This mixture is treated with 10 parts by weight of a solvent mixtureconsisting of 80% by wt. of normal hexane 20% by wt. of isopropanol Thismixture is maintained at 60 C for 15 minutes and solvent is drawn off,finally under vacuum.

The washingwith this solvent mixture is repeated several times. Finallythe yeast product is dried in sufollowing Table: 30 perheated steam.

TABLE Run No. 4 7 8 Solvent and- Ethanol (20 hours) Period of treatmentEthanol (ll hours) Hexane 9 hours) lsogropanol hours) Rate of Feed ofSolvent 600 whr. 600 mls/hr. 600 ml L hr. Temperature C 60C 60C Weightof Yeast Paste (grams) 1000 I000 1000 Analysis Before After Before AfterBefore After Treatment Treatment Treatment Treatment Treatment TreatmentDry Yeast Wt. (grams) 210 140 210 200 210 200 Nitrogen 6.0t 9.0 5.657.45 5.65 8.50 Total wt. of

Lipids in Yeast 41.2 5.0 42.9 4.2 42.9 6.9 Extract Wt. (grams) 72 200EXAMPLE 4 EXAMPLE 5 A yeast of the strain Hansenulasuaveolens is grownin continuous culture at a dilution rate of 0.2 vol/vollhour onparaffinic gas oil asfeedstock using a concentration of said gas oil ofgrams/litre, a temperature of 30 C and a nutrient medium (containingsodium phosphate, potassium chloride, magnesium sulphate and ammoniumsulphate) as described in Example 1. Start-up procedure using the saidstrain of yeast is otherwise as described in Example 1.

The pH is maintained at a value of 4 by continuous addition ofcontrolled amounts of aqueous ammonia.

The growth rate is ofthe order of 10 grams/litre. The broth thusobtained, containing yeast contaminated with some unmetabolisedfeedstock and aqueous nutrient, is centrifuged in order to obtain ayeast cream. This yeast cream is then treated with an aqueous me- Theprocess described in Example 4 was repeated using a strain of Candidautilis and a satisfactoryyeast product recovered.

EXAMPLE 6 l.6 grams NaCl 0.02 grams MgSO .7H,O 0.48 grams NH C| 4.6grams hard water containing minerals in trace amounts l00 mls mls mgm.

' The growth rate is of the order of grams/litre. The broth thusobtained, containing bacteria contaminated with some unmetabolisedfeedstock and aqueous nutrient, is submitted to centrifuging. Thefraction containing the micro-organism is subjected to treatment with anaqueous treating medium containing a surface active agent, using 0.5grams/litre of a surface active agent consisting of 1 mole of lauricalcohol condensed with 8.75 moles of ethylene oxide. The mixture wassubjected to centrifuging in a Sharples Supercentrifuge (of tubulartype) and the micro-organism fraction so obtained is afterwards washedwith tap water. The cream containing 1 part by weight of bacteria(estimated at dry weight after drying at 120 C) and 3 to 4 parts ofwater is charged to a solvent extraction drum with 8 parts ofisopropanol. The mixture is maintained at 60 C for 30 minutes whilerotating the drum.

Solvent is drawn off, finally under vacuum. There is thus obtained amixture of 2 parts of dry matter and 2 parts of solvent which consistedof /a water and of isopropanol together with some remainingcontaminants.

This mixture was treated with 10 parts by weight of a solvent mixtureconsisting of 80% by wt. by wt.

Normal hexane lsopropanol EXPERIMENT l The process described in Example1 was repeated except that the yeast employed was a yeast Saccharomycescerevisiae cultivated in the known manner on a substratum of beetmolasses. It is found that no perceptible improvement in thecharacteristic taste of this yeast is obtained.

EXPERIMENT 2 A similar experiment is carried out starting off from ayeast Torula cultivated in a known manner on cellulose bisulphiteliquor. It is found in like manner that no perceptible improvement inthe characteristic taste of this yeast is obtained.

We claim:

1. A process which comprises cultivating a straight chain paraffinichydrocarbon-consuming microorganism in the presence of a feedstockconsisting at least in part of a straight chain hydrocarbon, recoveringa fraction comprising the micro-organism and at least some aqueousmedium and residual hydrocarbon, mixing said fraction with a surfaceactive agent and treating the mixture to recover (a) a washed fractioncomprising the micro-organism together with an aqueous phase and someresidual hydrocarbon fraction and (b) a hydrocarbon fraction of reducedcontent of straight chain paraffins or which is free of normalparaffins; the said washed fractionbeing treated by solvent extractionfor the removal, at least in part, from the microorganism of lipidstogether with hydrocarbons associated with said micro-organism.

2. A process which comprises cultivating a straight chain paraffinichydrocarbon-consuming microorganism in the presence of a feedstockconsisting at least in part of a straight chain hydrocarbon, recoveringa fraction comprising the micro-organism and at least some aqueousmedium and residual hydrocarbon, mixing said fraction with a surfaceactive agent and treating the mixture to recover (a).a washed fractioncomprising the micro-organism together with an aqueous phase and someresidual hydrocarbon fraction and (b) a hydrocarbon fraction of reducedcontent of straight chain paraffins or which is free of normal paraffinsand thereafter a micro-organism containing fraction derived from saidwashed fraction being treated by solvent extraction for the removal, atleast in part, from the micro-organism of lipids together withhydrocarbons associated with said micro-organism.

3. A process according to claim 1 in which the straight chain paraffinichydrocarbon-consuming micro-organism is a yeast.

4. .A process according to claim 3 in which the yeast is of the familyCryptococcaceae.

5. A process according to claim 4 in which the yeast is of the subfamilyCryptococcoideae.

6. A process accordingto claim 5 in which the yeast is of the genusTorulopsis.

7. A process according to claim 5 in which the yeast is of the genusCandida.

8. A process according to claim 7 in which the yeast is Candidalipolytica.

9. A process according to claim 1 in which the microorganism is abacterium.

10. A process according to claim 1 in which the solvent extraction iseffected by means of a solvent comprising a hydrocarbon.

11. A process according to claim 10 in which the solvent comprising ahydrocarbon is a mixture of a hydrocarbon and a polar solvent.

12. A process according to claim 11 in which the polar solvent is analcohol.

13. A process according to claim 12 in which the polar solvent isethanol.

14. A process according to claim 12 in which the polar solvent isisopropanol.

15. A process according to claim 11in which the hydrocarbon is normalhexane.

16. A process according to claim 11 in which the hydrocarbon is benzene.

17. A process according to claim 11 in which the hydrocarbon is a lightplatformate fraction.

18. A process according to claim 11 in which the mixed hydrocarbon andpolar solvent is an azeotropic mixture.

19. A process which comprises cultivating a straight chain paraffinichydrocarbon-consuming yeast in the presence of a feedstock consisting atleast in part of a straight chain hydrocarbon, recovering a fractioncomprising the yeast and at least some aqueous medium and residualhydrocarbon, mixing said fraction with a surface active agent,subjecting the mixture to a phase separation to recover (a) a treatedfraction comprising the yeast together with an aqueous phase and someresidual hydrocarbon fraction and (b) a hydrocarbon fraction andsubjecting the said treated fraction to solvent extraction to remove apart of the lipids and associated hydrocarbons from said yeast.

1. A PROCESS WHICH COMPRISES CULTIVATING A STRAIGHT CHAIN PARAFFINICHYDROCARBON-CONSUMING MICRO-ORGANISM IN THE PRESENCE OF A FEEDSTOCKCONSISTING AT LEAST IN PART OF A STRAIGHT CHAIN HYDROCARBON, RECOVERINGA FRACTION COMPRISING THE MICRO-ORGANISM AND AT LEAST SOME AQUEOUSMEDIUM AND RESIDUAL HYDROCARBON, MIXING SAID FRACTION WITH A SURFACEACTIVE AGENT AND TREATING THE MIXTURE TO RECOVER (A) A WASHED FRACTIONCOMPRISING THE MICRO-ORGANISM TOGETHER WITH AN AQUEOUS PHASE AND SOMERESIDUAL HYDROCARBON FRACTION AND (B) A HYDROCARBON FRACTION OF REDUCEDCONTENT OF STRAIGHT CHAIN PARAFFINS OR WHICH IS FREE OF NORMALPARAFFINS; THE SAID WASHED FRACTION BEING TREATED BY SOLVENT EXTRACTIONFOR THE REMOVAL, AT LEAST IN PART, FROM THE MICRO-ORGANISM OF LIPIDSTOGETHER WITH HYDROCARBONS ASSOCIATED WITH SAID MICRO-ORGANISM.
 2. Aprocess which comprises cultivating a straight chain paraffinichydrocarbon-consuming micro-organism in the presence of a feedstockconsisting at least in part of a straight chain hydrocarbon, recoveringa fraction comprising the micro-organism and at least some aqueousmedium and residual hydrocarBon, mixing said fraction with a surfaceactive agent and treating the mixture to recover (a) a washed fractioncomprising the micro-organism together with an aqueous phase and someresidual hydrocarbon fraction and (b) a hydrocarbon fraction of reducedcontent of straight chain paraffins or which is free of normal paraffinsand thereafter a micro-organism containing fraction derived from saidwashed fraction being treated by solvent extraction for the removal, atleast in part, from the micro-organism of lipids together withhydrocarbons associated with said micro-organism.
 3. A process accordingto claim 1 in which the straight chain paraffinic hydrocarbon-consumingmicro-organism is a yeast.
 4. A process according to claim 3 in whichthe yeast is of the family Cryptococcaceae.
 5. A process according toclaim 4 in which the yeast is of the subfamily Cryptococcoideae.
 6. Aprocess according to claim 5 in which the yeast is of the genusTorulopsis.
 7. A process according to claim 5 in which the yeast is ofthe genus Candida.
 8. A process according to claim 7 in which the yeastis Candida lipolytica.
 9. A process according to claim 1 in which themicro-organism is a bacterium.
 10. A process according to claim 1 inwhich the solvent extraction is effected by means of a solventcomprising a hydrocarbon.
 11. A process according to claim 10 in whichthe solvent comprising a hydrocarbon is a mixture of a hydrocarbon and apolar solvent.
 12. A process according to claim 11 in which the polarsolvent is an alcohol.
 13. A process according to claim 12 in which thepolar solvent is ethanol.
 14. A process according to claim 12 in whichthe polar solvent is isopropanol.
 15. A process according to claim 11 inwhich the hydrocarbon is normal hexane.
 16. A process according to claim11 in which the hydrocarbon is benzene.
 17. A process according to claim11 in which the hydrocarbon is a light platformate fraction.
 18. Aprocess according to claim 11 in which the mixed hydrocarbon and polarsolvent is an azeotropic mixture.
 19. A process which comprisescultivating a straight chain paraffinic hydrocarbon-consuming yeast inthe presence of a feedstock consisting at least in part of a straightchain hydrocarbon, recovering a fraction comprising the yeast and atleast some aqueous medium and residual hydrocarbon, mixing said fractionwith a surface active agent, subjecting the mixture to a phaseseparation to recover (a) a treated fraction comprising the yeasttogether with an aqueous phase and some residual hydrocarbon fractionand (b) a hydrocarbon fraction and subjecting the said treated fractionto solvent extraction to remove a part of the lipids and associatedhydrocarbons from said yeast.